1. Field of the Invention
The present invention relates generally to a system and method for detecting, imaging, and determining the location of objects in a turbid medium using light as a probe, and more particularly relates to a system and method for finding and locating objects including, tumors in living tissue, an individual, a building, or a vehicle such as an aircraft, a missile, etc. located in smoke, fog, and vehicles and objects such as submarines and mines located in shallow and/or murky water using independent component analysis (ICA).
2. Description of the Related Art
With the pervasiveness of cancer and terrorism in modern times, it has become common to screen for undesired objects. For example, it is common to screen the human body for tumors which can include cancerous as well as benign tumors. Moreover, with the pervasiveness of terrorism, it is common to patrol and screen secure areas for objects and individuals that should not be in the secure areas. For example, border crossings, military bases, airports, governmental buildings, high-occupancy buildings and other selected locations are typically under constant surveillance to assure the security of these areas. Finding objects in a turbid medium has been researched in the past. Basic principles and simulation as well as experimental results of finding objects in a turbid medium are known. For example, see M. Xu et al. “Simulated And Experimental Separation And Characterization Of Absorptive Inhomogeneities Embedded In Turbid Media,” OSA Biomedical Topical Meeting, April, 2004; M. Alrubaiee et al. “Time-Resolved And Quasi-Continuous Wave Three-Dimensional Tomographic Imaging,” Femtosecond Laser Applications in Biology, Proceedings of SPIE, vol. 5463, April, 2004; M. Xu et al. “Information Theory Approach To Detect Small Inhomogeneities Within Tissue-Like Turbid Media,” the 4th Inter-institute Workshop on Optical Diagnostic Imaging from Bench to Bedside, National Institutes of Health, Natcher Conference Center, Sep. 20-22, 2004; M. Alrubaiee et al. “Three-Dimensional Localization And Reconstruction Of Objects In A Turbid Medium Using Independent Component Analysis Of Optical Transmission And Fluorescence Measurements,” the 4th Inter-institute Workshop on Optical Diagnostic Imaging from Bench to Bedside, National Institutes of Health, Sep. 20-22, 2004, the contents of all of which are incorporated herein by reference.
Additionally, on the medical side, noninvasive optical probing of tumors and functional monitoring of physiological activities in a human body using near infrared (NIR) light has been investigated by many investigators as compiled in G. Muller, R. R. Alfano, et al. Medical Optical Tomography: Functional Imaging and Monitoring, Vol. IS11 of SPIE Institute Series, 1993; S. K. Gayen and R. R. Alfano, “Emerging Optical Biomedical Imaging Techniques,” Opt. Photon. News 7, 17-22 1996; J. C. Hebden, et al. “Optical Imaging In Medicine: I. Experimental Techniques,” Phys. Med. Biol. 42, 825-840, 1997; S. R. Arridge et al., “Optical Imaging In Medicine: II. Modeling And Reconstruction,” Phys Med Biol. 42, 841-853, 1997, the contents of all of which are incorporated herein by reference. While some optical imaging techniques use a difference in light scattering and absorption characteristics between normal and cancerous tissues, other optical image techniques detect fluorescence of externally administered contrast agents that attach selectively to the tumors, or native tissue fluorescence. For example, see Ntziachristos et al., “Experimental Three-Dimensional Fluorescence Reconstruction Of Diffuse Media By Use Of A Normalized Born Approximation,” Opt. Lett. 26, 893-895, (2001); A. B. Milstein, et al., “Fluorescence Optical Diffusion Tomography,” Appl. Opt. 42, 3081-3094 (2003), the contents of all which are incorporated herein by reference.
Although both direct imaging, for example as disclosed in L. Wang, R. R. Alfano et al., “Ballistic 2-D Imaging Through Scattering Walls Using An Ultrafast Optical Kerr Gate,” Science 253, 769-771, 1991, and inverse reconstruction, for example as disclosed in R. Arridge, “Optical Tomography In Medical Imaging,” Inverse Problems 15, R41-R93, 1999, approaches have been used to obtain images of a target embedded in various types of turbid media, these methods still leave much to be desired. For example, the direct imaging approach uses different techniques to sort out image bearing ballistic and snake light, and to reject image blurring multiple scattered light in order to obtain a desired image, for example see U.S. Pat. No. 5,140,463, entitled “Method And Apparatus For Improving The Signal To Noise Ratio Of An Image Formed Of An Object Hidden In Or Behind A Semi-Opaque Random Media,” to Yoo et. al.; U.S. Pat. No. 5,142,372, to R. R. Alfano et. al., entitled U.S. Pat. No. 5,227,912, entitled “Multiple-Stage Optical Kerr Gate System,” to Ho et. al., U.S. Pat. No. 5,371,368, entitled “Ultrafast Optical Imaging Of Objects In A Scattering Medium,” to R. R. Alfano et. al.; Gayen and R. R. Alfano, “Sensing Lesions In Tissues With Light,” Optics Express Vol. 4, pp. 475-480 (1999); Gayen et. al., “Two-Dimensional Near-Infrared Transillumination Imaging Of Biomedical Media With A Chromium-Doped Forsterite Laser,” Appl. Opt. Vol. 37, pp. 5327-5336 (1998); Gayen, et. al. “Near-Infrared Laser Spectroscopic Imaging: A Step Towards Diagnostic Optical Imaging Of Human Tissues,” Lasers in the Life Sciences Vol. 37, pp. 187-198, (1999); Gayen, et. al., “Time-Sliced Transillumination Imaging Of Normal And Cancerous Breast Tissues,” in OSA Trends in Optics and Photonics Series Vol. 21 on Advances in Optical Imaging and Photon Migration, pp. 63-66, (1998); Dolne et. al, “IR Fourier Space Gate And Absorption Imaging Through Random Media,” Lasers in the Life Sciences Vol. 6, pp. 131-141, (1994); Das et. al. “Ultrafast Time-Gated Imaging In Thick Tissues: A Step Toward Optical Mammography,” Opt. Lett. Vol. 18, pp. 1002-1004, (1993); Hebden et. al., “Time Resolved Imaging Through A Highly Scattering Medium,” Appl. Opt. Vol. 30, pp. 788-794, (1991); and Demos et. al., “Time-Resolved Degree Of Polarization For Human Breast Tissue,” Opt. Commun. Vol. 124, pp. 439-442, (1996); the contents of all of which is incorporated herein by reference.
Although the above disclosed methods are typically suitable for turbid mediums whose thickness is less than 10 times the transport-mean-free-path, it is now accepted that for the turbid medium thickness which is greater than 10 times the transport-mean-free-path, direct shadowgram imaging is not feasible, and one has to resort to inverse reconstruction technique.
The conventional inverse reconstruction approach to locate and characterize the targets, matches the detected light intensities on the boundaries to that computed by a forward model of light propagation in the medium. The absorption and scattering coefficient distribution of the full medium is updated iteratively until the emerging light intensities on the boundaries predicted by the forward model are close to the observed values. Various approaches using time-resolved, frequency-domain, or steady-state lasers have been explored for inverse image reconstruction. Examples of inverse reconstruction methods include U.S. Pat. No. 5,813,988, entitled “Time-Resolved Diffusion Tomographic Imaging In Highly Scattering Turbid Media,” to R. R. Alfano et. al.; U.S. Pat. No. 5,931,789, entitled “Time-Resolved Diffusion Tomographic 2d And 3d Imaging In Highly Scattering Turbid Media,” to R. R. Alfano et. al.; Cai et. al., “Optical Tomographic Image Reconstruction From Ultrafast Time-Sliced Transmission Measurements,” Appl. Opt. Vol. 38, pp. 4237-4246 (1999); Cai et. al., “Time-Resolved Optical Diffusion Tomographic Image Reconstruction In Highly Scattering Turbid Media,” Proc. Natl. Acad. Sci. USA, Vol. 93, pp. 13561-13564, (1996); U.S. Pat. No. 6,665,557 B1, entitled “Sprectroscopic And Time-Resolved Optical Methods And Apparatus For Imaging Objects In Turbed Media,” to R. R. Alfano et. al.; S. R. Arridge, “The Forward And Inverse Problems In Time-Resolved Infrared Imaging,” published in the Medical Optical Tomography: Functional Imaging and Monitoring, SPIE, vol. IS11, C. Muller ed., PP. 31-64, (1993); and Singer et. al., “Image Reconstruction Of Interior Bodies That Diffuse Radiation,” Science, Vol. 248, pp 990-993, (1993); the contents of each of which are incorporated herein by reference.